Induction of DNA damage by dimethylarsine, a metabolite of inorganic arsenics, is for the major part likely due to its peroxyl radical

Hepatoprotective role of vitamin B(12) and folic acid in arsenic intoxicated rats

The present study elucidated the protective role of vitamin B(12) with folic acid against arsenic-induced hepatotoxicity in female rats. Ingestion of sodium-arsenite- contaminated water [0.4 ppm/100 g body weight (b.w.)/day] in combination with vitamin B(12) plus folic acid (0.07 and 4.0 μg, respectively/100 g b.w./day) for 24 days to Wistar rats offered a significant protection against alone arsenic-induced distorted liver function, damaged histoarchitecture, elevated oxidative stress, and DNA fragmentation of hepatic tissues. Arsenic only exposure decreased hepatic superoxide dismutase (SOD), catalase activities, and the level of nonprotein-soluble thiol (NPSH), with a concomitant increase in thiobarbituric acid reactive substances (TBARS) and conjugated dienes (CDs) in the liver. Vitamin supplementation restrained the increase of TBARS and CDs by restoring catalase, SOD, and NPSH levels. Restricted generation of free radicals may be correlated to the protection of DNA stability and hepatic morphology. This study explains the decisive role of vitamin B(12) with folic acid to ameliorate arsenic-mediated liver injuries.

Protective role of Moringa oleifera (Sajina) seed on arsenic-induced hepatocellular degeneration in female albino rats

In an attempt to develop new herbal therapy, an aqueous extract of the seed of Moringa oleifera was used to screen the effect on arsenic-induced hepatic toxicity in female rat of Wistar strain. Subchronic exposure to sodium arsenite (0.4 ppm/100 g body weight/day via drinking water for a period of 24 days) significantly increased activities of hepatic and lipid function markers such as alanine transaminase, aspartate transaminase, cholesterol, triglycerides, LDL along with a decrease in total protein and HDL. A notable distortion of hepatocellular histoarchitecture was prominent with a concomitant increase in DNA fragmentation following arsenic exposure. A marked elevation of lipid peroxidation in hepatic tissue was also evident from the hepatic accumulation of malondialdehyde and conjugated dienes along with suppressed activities in the antioxidant enzymes such as superoxide dismutase and catalase. However, co-administration of aqueous seed extract of M. oleifera (500 mg/100 g body weight/day for a period of 24 days) was found to significantly prevent the arsenic-induced alteration of hepatic function markers and lipid profile. Moreover, the degeneration of histoarchitecture of liver found in arsenic-treated rats was protected along with partial but definite prevention against DNA fragmentation induction. Similarly, generation of reactive oxygen species and free radicals were found to be significantly less along with restored activities of antioxidant enzymes in M. oleifera co-administered group with comparison to arsenic alone treatment group. The present investigation offers strong evidence for the hepato-protective and antioxidative efficiencies of M. oleifera seed extract against oxidative stress induced by arsenic.

Arsenic-induced oxidative stress and its reversibility

This review summarizes the literature describing the molecular mechanisms of arsenic-induced oxidative stress, its relevant biomarkers, and its relation to various diseases, including preventive and therapeutic strategies. Arsenic alters multiple cellular pathways including expression of growth factors, suppression of cell cycle checkpoint proteins, promotion of and resistance to apoptosis, inhibition of DNA repair, alterations in DNA methylation, decreased immunosurveillance, and increased oxidative stress, by disturbing the pro/antioxidant balance. These alterations play prominent roles in disease manifestation, such as carcinogenicity, genotoxicity, diabetes, cardiovascular and nervous systems disorders. The exact molecular and cellular mechanisms involved in arsenic toxicity are rather unrevealed. Arsenic alters cellular glutathione levels either by utilizing this electron donor for the conversion of pentavalent to trivalent arsenicals or directly binding with it or by oxidizing glutathione via arsenic-induced free radical generation. Arsenic forms oxygen-based radicals (OH(•), O(2)(•-)) under physiological conditions by directly binding with critical thiols. As a carcinogen, it acts through epigenetic mechanisms rather than as a classical mutagen. The carcinogenic potential of arsenic may be attributed to activation of redox-sensitive transcription factors and other signaling pathways involving nuclear factor κB, activator protein-1, and p53. Modulation of cellular thiols for protection against reactive oxygen species has been used as a therapeutic strategy against arsenic. N-acetylcysteine, α-lipoic acid, vitamin E, quercetin, and a few herbal extracts show prophylactic activity against the majority of arsenic-mediated injuries in both in vitro and in vivo models. This review also updates the reader on recent advances in chelation therapy and newer therapeutic strategies suggested to treat arsenic-induced oxidative damage.

Therapeutic efficacy of silymarin and naringenin in reducing arsenic-induced hepatic damage in young rats

We investigated the effects of silymarin and naringenin in counteracting arsenic-induced hepatic oxidative stress post exposure. Male wistar rats were chronically exposed to sodium arsenite for eight months followed by oral treatment with silymarin and naringenin (50 mg/kg each) for 15 consecutive days to evaluate hepatic damage and antioxidant potential. Our results demonstrate a significant decrease in hepatic GSH levels, SOD and catalase activities and an increase in GST and TBARS levels after arsenic administration. Silymarin or naringenin administration increased GSH levels and was beneficial in the recovery of altered SOD and catalase activity besides significantly reducing blood and tissue arsenic concentration. Our results point to the antioxidant potential of these flavonoids, which might be of benefit in the clinical recovery of subject exposed to arsenic. These flavonoids can be incorporated into the diet or co-supplemented during chelation treatment, and thus may afford a protective effect against arsenite-induced cytotoxicity.

Superoxide dismutase protects cells from DNA damage induced by trivalent methylated arsenicals

Superoxide dismutase (SOD) catalyzes the conversion of superoxide to hydrogen peroxide. Heterozygous mice of strain B6;129S7-Sod1(tm1Leb)/J were obtained from Jackson Laboratories and bred to produce offspring that were heterozygous (+/Sod1(tm1Leb)), homozygous wild-type (+/+), and homozygous knockout (Sod1(tm1Leb) /Sod1(tm1Leb)) for the Cu/Zn superoxide dismutase (Sod1) gene. Splenocytes from these mice were exposed to several concentrations of either sodium arsenite (As3 [0-200 μM]), monomethylarsonous acid (MMA3 [0-10 μM]), or dimethylarsinous acid (DMA3 [0-10 μM]) for 2 hr. Cells were then examined for DNA damage using the alkaline single cell gel electrophoresis assay. Methyl methanesulfonate (MMS) was used as a positive control. Splenocytes from each of the three genotypes for Sod1 were equally sensitive to MMS and As3. However, at equimolar concentrations, DMA3 and MMA3 produced significantly more DNA damage in the homozygous knockout mouse splenocytes than in the splenocytes from the wild-type or heterozygous mice. These findings suggest that superoxide is involved either directly or indirectly in producing DNA damage in cells exposed to trivalent methylated arsenicals. These arsenicals may generate reactive oxygen species that damage DNA. This DNA damage may be a key factor in initiating cancer in vivo.

Chronic exposure to low levels of inorganic arsenic causes alterations in locomotor activity and in the expression of dopaminergic and antioxidant systems in the albino rat

Several studies have associated chronic arsenicism with decreases in IQ and sensory and motor alterations in humans. Likewise, studies of rodents exposed to inorganic arsenic ((i)As) have found changes in locomotor activity, brain neurochemistry, behavioral tasks, oxidative stress, and in sensory and motor nerves. In the current study, male Sprague-Dawley rats were exposed to environmentally relevant doses of (i)As (0.05, 0.5 mg (i)As/L) and to a high dose (50 mg (i)As/L) in drinking water for one year. Hypoactivity and increases in the striatal dopamine content were found in the group treated with 50 mg (i)As/L. Exposure to 0.5 and 50 mg (i)As/L increased the total brain content of As. Furthermore, (i)As exposure produced a dose-dependent up-regulation of mRNA for Mn-SOD and Trx-1 and a down-regulation of DAR-D₂ mRNA levels in the nucleus accumbens. DAR-D₁ and Nrf2 mRNA expression were down-regulated in nucleus accumbens in the group exposed to 50 mg (i)As/L. Trx-1 mRNA levels were up-regulated in the cortex in an (i)As dose-dependent manner, while DAR-D₁ mRNA expression was increased in striatum in the 0.5 mg (i)As/L group. These results show that chronic exposure to low levels of arsenic causes subtle but region-specific changes in the nervous system, especially in antioxidant systems and dopaminergic elements. These changes became behaviorally evident only in the group exposed to 50 mg (i)As/L.

Cellular uptake, subcellular distribution and toxicity of arsenic compounds in methylating and non-methylating cells

Arsenic is a known human carcinogen, inducing tumors of the skin, urinary bladder, liver and lung. Inorganic arsenic, existing in highly toxic trivalent and significantly less toxic pentavalent forms, is methylated to mono- and di-methylated species mainly in the liver. Due to the low toxicity of pentavalent methylated species, methylation has been regarded as a detoxification process for many years; however, recent findings of a high toxicity of trivalent methylated species have indicated the contrary. In order to elucidate the role of speciation and methylation for the toxicity and carcinogenicity of arsenic, systematic studies were conducted comparing cellular uptake, subcellular distribution as well as toxic and genotoxic effects of organic and inorganic pentavalent and trivalent arsenic species in both non-methylating (urothelial cells and fibroblasts) and methylating cells (hepatocytes). The membrane permeability was found to be dependent upon both the arsenic species and the cell type. Uptake rates of trivalent methylated species were highest and exceeded those of their pentavalent counterparts by several orders of magnitude. Non-methylating cells (urothelial cells and fibroblasts) seem to accumulate higher amounts of arsenic within the cell than the methylating hepatocytes. Cellular uptake and extrusion seem to be faster in hepatocytes than in urothelial cells. The correlation of uptake with toxicity indicates a significant role of membrane permeability towards toxicity. Furthermore, cytotoxic effects are more distinct in hepatocytes. Differential centrifugation studies revealed that elevated concentrations of arsenic are present in the ribosomal fraction of urothelial cells and in nucleic and mitochondrial fractions of hepatic cells. Further studies are needed to define the implications of the observed enrichment of arsenic in specific cellular organelles for its carcinogenic activity. This review summarizes our recent research on cellular uptake, distribution and toxicity of arsenic compounds in methylating and non-methylating cells.

The involvement of hypophyseal-gonadal and hypophyseal-adrenal axes in arsenic-mediated ovarian and uterine toxicity: modulation by hCG

This study evaluated the involvement of hypophyseal-gonadal and hypophyseal-adrenal axes as a possible mechanism of sodium arsenite toxicity in ovary and uterus by the coadministration of hCG. Subchronic treatment of 0.4 ppm of sodium arsenite/(100 g body weight day) via drinking water for seven estrous cycles significantly suppressed the plasma levels of leutinizing hormone, follicle-stimulating hormone, and estradiol along with sluggish ovarian activities of Delta(5),3beta-hydroxysteroid dehydrogenase and 17beta-hydroxysteroid dehydrogenase followed by a reduction in gonadal tissue peroxidase activities in mature female rats at diestrous phase. Noticeable weight loss of the ovary and uterus along with prolonged diestrous phase and increased deposition of arsenic in the plasma and in these reproductive organs were also demonstrated following the ingestion of arsenic. Follicular atresia and thinning of the uterine luminal diameter were evident after sodium arsenite treatment. Effective protection of gonadal weight loss, suppressed ovarian steroidogenesis, and altered ovarian and uterine peroxidase activities were noticed when 1.0 IU hCG/(100 g body weight day) is given in arsenic-intoxicated rats. Normal estrous cyclicity was restored toward the control level after hCG coadministration, though the elimination of elementary arsenic from the plasma and gonadal tissues was impossible. A significant recovery in the restoration of ovarian and uterine histoarchitecture was prominent after hCG treatment. Adrenal hypertrophy and steroidogenic arrest of the adrenal gland along with altered level of brain monoamines in the midbrain and diencephalons following arsenic intoxication were also ameliorated after hCG coadministration.

The role of oxidative stress in carcinogenesis induced by metals and xenobiotics

In addition to a wide range of adverse effects on human health, toxic metals such as cadmium, arsenic and nickel can also promote carcinogenesis. The toxicological properties of these metals are partly related to generation of reactive oxygen species (ROS) that can induce DNA damage and trigger redox-dependent transcription factors. The precise mechanisms that induce oxidative stress are not fully understood. Further, it is not yet known whether chronic exposures to low doses of arsenic, cadmium or other metals are sufficient to induce mutations in vivo, leading to DNA repair responses and/or tumorigenesis. Oxidative stress can also be induced by environmental xenobiotics, when certain metabolites are generated that lead to the continuous release of superoxide, as long as the capacity to reduce the resulting dions (quinones) into hydroquinones is maintained. However, the specific significance of superoxide-dependent pathways to carcinogenesis is often difficult to address, because formation of DNA adducts by mutagenic metabolites can occur in parallel. Here, we will review both mechanisms and toxicological consequences of oxidative stress triggered by metals and dietary or environmental pollutants in general. Besides causing DNA damage, ROS may further induce multiple intracellular signaling pathways, notably NF-kB, JNK/SAPK/p38, as well as Erk/MAPK. These signaling routes can lead to transcriptional induction of target genes that could promote proliferation or confer apoptosis resistance to exposed cells. The significance of these additional modes depends on tissue, cell-type and is often masked by alternate oncogenic mechanisms being activated in parallel.

Methylated Metal(loid) Species in Humans

While the metal(loid)s arsenic, bismuth, and selenium (probably also tellurium) have been shown to be enzymatically methylated in the human body, this has not yet been demonstrated for antimony, cadmium, germanium, indium, lead, mercury, thallium, and tin, although the latter elements can be biomethylated in the environment. Methylated metal(loid)s exhibit increased mobility, thus leading to a more efficient metal(loid) transport within the body and, in particular, opening chances for passing membrane barriers (blood-brain barrier, placental barrier). As a consequence human health may be affected. In this review, relevant data from the literature are compiled, and are discussed with respect to the evaluation of assumed and proven health effects caused by alkylated metal(loid) species.

Association of arsenic and kidney dysfunction in people with diabetes and validation of its effects in rats

We studied villagers with and without diabetes from arsenic-endemic areas and a nearby control site in Xinjiang Autonomous Region, PR China. Water and urinary arsenic were assayed for exposure measurement. Urinary NAG (N-acetyl-beta-glucosaminidase), a kidney function test, blood glucose, triglyceride, cholesterol, high density lipid and low density lipid were measured. Villagers from endemic areas were found to have higher urinary arsenic concentrations. The NAG results also suggest that chronic arsenic exposure presents a significant adverse impact on the kidney function of villagers in the endemic areas. However, blood glucose levels of diabetes individuals were lower than those from the control site. These observations were validated in rats which were chronically exposed to arsenic in drinking water. The distinct relationship between chronic arsenic exposure and diabetes mellitus requires further investigation. A rodent model is a useful tool for study of this type.

Arsenicosis status and urinary malondialdehyde (MDA) in people exposed to arsenic contaminated-coal in China

The current arsenic exposure condition, arsenicosis prevalence, urinary arsenic and MDA (malondialdehyde) concentrations in people were studied. The study area, a village in Xing Ren County in Guizhou Province, PR China, is a coal-borne arsenicosis endemic area that was identified several decades ago. The residents in Xing Ren have been using coal containing high arsenic levels all their life. Urinary arsenic levels of villagers were 192.2+/-22 microg/g creatinine (n=113) in the coal-borne endemic area (Xing Ren county) and were significantly higher than 63.6+/-5.9 microg/g creatinine (n=30) in a neighbouring control site (a village in Xing Yi county). The urinary MDA concentrations of villagers from the endemic area were also significantly higher compared to those of the control area. There was a strong correlation between age and urinary arsenic and MDA concentrations in the endemic area of Xing Ren; urinary arsenic and MDA levels decreased with age. Fifty out of 113 (44.3%) villagers in the endemic area had arsenicosis symptoms and the prevalence in villagers older than 40 y was 100% in male (92.2% overall). Urinary MDA concentration was significantly higher in people with arsenicosis symptoms in the endemic areas. Oxidative stress (urinary MDA concentration) was strongly related to arsenic exposure but not to the age and smoking habit. Higher urinary arsenic and MDA levels in younger villagers from the endemic area suggest that they are having a higher exposure to coal-borne emitted arsenic because they spend more time indoor. There is an urgent need to develop proper intervention methods in the Guizhou endemic areas in order to reduce the risk to the local communities who are still using arsenic contaminated-coal.

Ameliorating effect of curcumin on sodium arsenite-induced oxidative damage and lipid peroxidation in different rat organs

The present study was conducted to investigate the antioxidative effect of curcumin against sodium arsenite-induced oxidative damage in rat. Animals were divided into four groups, the first group was used as control. Groups 2, 3 and 4 were orally treated with curcumin (15 mg/kg BW), sodium arsenite (Sa, 5 mg/kg BW) and sodium arsenite plus curcumin, respectively. Rats were orally administered their respective doses daily for 30 days. Results showed that Sa increased thiobarbituric acid-reactive substances (TBARS) in plasma, liver, kidney, lung, testes and brain. While, the activities of glutathione S-transferase, superoxide dismutase and catalase and the content of sulfhydryl groups (SH-groups) were significantly decreased in plasma and tissues compared to control. Treatment with curcumin alone reduced the levels of TBARS, while induced the activities of the antioxidant enzymes, and the levels of SH-groups. The presence of curcumin with Sa reduced the induction in the levels of TBARS and induced the decrease in the activities of antioxidant enzymes and the levels of SH-groups. Results indicated that treatment with Sa decreased body weight and increased liver weight compared to control. The presence of curcumin with Sa alleviated its toxic effects. It can be concluded that curcumin has beneficial influences and could be able to antagonize Sa toxicity.

Methylated Arsenicals: The Implications of Metabolism and Carcinogenicity Studies in Rodents to Human Risk Assessment

Monomethylarsonic acid (MMA(V)) and dimethylarsinic acid (DMA(V)) are active ingredients in pesticidal products used mainly for weed control. MMA(V) and DMA(V) are also metabolites of inorganic arsenic, formed intracellularly, primarily in liver cells in a metabolic process of repeated reductions and oxidative methylations. Inorganic arsenic is a known human carcinogen, inducing tumors of the skin, urinary bladder, and lung. However, a good animal model has not yet been found. Although the metabolic process of inorganic arsenic appears to enhance the excretion of arsenic from the body, it also involves formation of methylated compounds of trivalent arsenic as intermediates. Trivalent arsenicals (whether inorganic or organic) are highly reactive compounds that can cause cytotoxicity and indirect genotoxicity in vitro. DMA(V) was found to be a bladder carcinogen only in rats and only when administered in the diet or drinking water at high doses. It was negative in a two-year bioassay in mice. MMA(V) was negative in 2-year bioassays in rats and mice. The mode of action for DMA(V)-induced bladder cancer in rats appears to not involve DNA reactivity, but rather involves cytotoxicity with consequent regenerative proliferation, ultimately leading to the formation of carcinoma. This critical review responds to the question of whether DMA(V)-induced bladder cancer in rats can be extrapolated to humans, based on detailed comparisons between inorganic and organic arsenicals, including their metabolism and disposition in various animal species. The further metabolism and disposition of MMA(V) and DMA(V) formed endogenously during the metabolism of inorganic arsenic is different from the metabolism and disposition of MMA(V) and DMA(V) from exogenous exposure. The trivalent arsenicals that are cytotoxic and indirectly genotoxic in vitro are hardly formed in an organism exposed to MMA(V) or DMA(V) because of poor cellular uptake and limited metabolism of the ingested compounds. Furthermore, the evidence strongly supports a nonlinear dose-response relationship for the biologic processes involved in the carcinogenicity of arsenicals. Based on an overall review of the evidence, using a margin-of-exposure approach for MMA(V) and DMA(V) risk assessment is appropriate. At anticipated environmental exposures to MMA(V) and DMA(V), there is not likely to be a carcinogenic risk to humans.

Evaluation of cell types for assessment of cytogenetic damage in arsenic exposed population

BACKGROUND

Cytogenetic biomarkers are essential for assessing environmental exposure, and reflect adverse human health effects such as cellular damage. Arsenic is a potential clastogen and aneugen. In general, the majority of the studies on clastogenic effects of arsenic are based on frequency of micronuclei (MN) study in peripheral lymphocytes, urothelial and oral epithelial cells. To find out the most suitable cell type, here, we compared cytogenetic damage through MN assay in (a) various populations exposed to arsenic through drinking water retrieved from literature review, as also (b) arsenic-induced Bowen's patients from our own survey.

RESULTS

For literature review, we have searched the Pubmed database for English language journal articles using the following keywords: "arsenic", "micronuclei", "drinking water", and "human" in various combinations. We have selected 13 studies consistent with our inclusion criteria that measured micronuclei in either one or more of the above-mentioned three cell types, in human samples. Compared to urothelial and buccal mucosa cells, the median effect sizes measured by the difference between people with exposed and unexposed, lymphocyte based MN counts were found to be stronger. This general pattern pooled from 10 studies was consistent with our own set of three earlier studies. MN counts were also found to be stronger for lymphocytes even in arsenic-induced Bowen's patients (cases) compared to control individuals having arsenic-induced non-cancerous skin lesions.

CONCLUSION

Overall, it can be concluded that MN in lymphocytes may be superior to other epithelial cells for studying arsenic-induced cytogenetic damage.

Oral administration of diphenylarsinic acid, a degradation product of chemical warfare agents, induces oxidative and nitrosative stress in cerebellar Purkinje cells

A new clinical syndrome with prominent cerebellar symptoms in patients living in Kamisu City, Ibaraki Prefecture, Japan, is described. Since the patients ingested drinking water containing diphenylarsinic acid (DPA), a stable degradation product of both diphenylcyanoarsine and diphenylchloroarsine, which were developed for use as chemical weapons and cause severe vomiting and sneezing, DPA was suspected of being responsible for the clinical syndrome. The purpose of the present study was to elucidate prominent cerebellar symptoms due to DPA. The aim of the study was to determine if single (15 mg/kg) or continuous (5 mg/kg/day for 5 weeks) oral administration of DPA to ICR-strain mice induced oxidative and/or nitrosative stress in their brain. Significantly positive staining with malondialdehyde (MDA) and 3-nitrotyrosine (3-NT) was observed in the cerebellar Purkinje cells by repeated administration (5 mg/kg/day) with DPA for 5 weeks that led to the cerebellar symptoms from a behavioral pharmacology standpoint and by single administration of DPA (15 mg/kg). Furthermore, it is possible that the production of 3-NT was not caused by peroxynitrite formation. The present results suggest the possibility that arsenic-associated novel active species may be a factor underlying the oxidative and nitrosative stress in Purkinje cells due to exposure to DPA, and that the damage may lead to the cerebellar symptoms.

Insights into the carcinogenic mode of action of arsenic

That arsenic can induce cancer in humans has been known since the late 17th century, yet how arsenic induces cancer has been the subject of numerous scientific publications. Various modes of action (MOA) have been proposed for arsenic's carcinogenicity. In this paper we review our previous studies on the ability of arsenicals to cause DNA damage, the relative inability of these arsenicals to induce point mutations, and the involvement of arsenicals in spindle disruption. We present new evidence that shows that reduced glutathione (GSH) can chemically reduce inactive pentavalent arsenicals to trivalent arsenicals which can disrupt tubulin polymerization, and show that reactive oxygen species (ROS) are most likely not involved in tubulin disruption. A hypothesis is also presented on how arsenic may induce stable chromosome aberrations (CAs) that can lead to cancer, thus supporting a role for genetic damage in the MOA for arsenic. We then propose promising areas of research that might give insight into the MOA of arsenic.

Carcinogenicity of dimethylarsinic acid in Ogg1-deficient mice

Oxidative stress to DNA is recognized as a mechanism underlying carcinogenic effects of some environmental agents. Here, we hypothesized that dimethylarsinic acid (DMA(V)), an organic metabolite of inorganic arsenic in humans, might exert carcinogenic potential in a mouse line carrying a mutant Mmh allele of the Mmh/OGG1 gene encoding the enzyme 8-hydroxyguanine DNA glycosylase 1 (OGG1). Ogg1 mutant and wild type mice were treated with DMA(V) in their drinking water at a dose of 200 p.p.m. for up to 72 weeks. All DMA(V)-treated Ogg1(-/-)animals developed tumors, with a tendency for lower total incidences in the Ogg1(+/+) cases. Lung tumors in particular were induced as compared to the lack in non-carcinogen controls and were significantly more frequent in the homozygotes. At week 4, the levels of DNA 8-OH-dG and cell proliferation were significantly elevated in the lungs of non-treated Ogg1(-/-) as compared to Ogg1(+/+) mice and were strongly enhanced by DMA(V) treatment. Marked induction of Pola1, Cyp7b1, Ndfua3, Mmp13 and other genes specific to cell proliferation, cell signaling and xenobiotic metabolism in the lungs of DMA(V)-treated Ogg1(-/-) mice was found. Electron microscopic examination revealed the growth of microvilli, with increased numbers of mitochondria only in lungs and lung tumors of DMA(V)-exposed Ogg1(-/-) mice. Therefore, we strongly suggest that DMA(V) exerts carcinogenicity in the lungs of Ogg1(-/-) mutant mice, with a possible role for persistent accumulation of DNA oxidative adducts.

Elevation of 8-hydroxydeoxyguanosine and cell proliferation via generation of oxidative stress by organic arsenicals contributes to their carcinogenicity in the rat liver and bladder

Monomethylarsonic acid (MMA(V)), dimethylarsinic acid (DMA(V)) and trimethylarsine oxide (TMAO(V)) are well-documented inorganic arsenic (iAs) methylated metabolites. In our previous studies, DMA(V) and TMAO(V) were shown to exert carcinogenicity in the rat bladder and liver, respectively. Furthermore, MMA(V), DMA(V) and TMAO(V) exhibited promoting activity on rat hepatocarcinogenesis. To clarify mechanisms of arsenical carcinogenicity and compare biological responses in the liver and bladder, male F344 rats were sequentially treated for 5, 10, 15, 20 days with MMA(V), DMA(V) and TMAO(V) in their drinking water at a dose of 0.02%. Significant increase of P450 total content and generation of hydroxyl radicals in the liver were observed from 10 and 15 days of treatment with arsenicals, respectively, with the highest levels induced by TMAO(V). Similarly, elevation of 8-hydroxy-2'-deoxyguanosine (8-OHdG) formation was found in the DNA with significant increase by TMAO(V) treatment in the liver at days 15 and 20, and DMA(V) in the bladder after 20 days treatment. In addition, cell proliferation and apoptosis indices were significantly increased by TMAO(V) in the liver and by DMA(V) in the bladder of rats. These events were accompanied by differential up-regulation of phase I and II metabolizing enzymes, cyclins D1 and E, PCNA, caspase 3 and FasL. The results indicate that early elevation of 8-OHdG and cell proliferation via generation of oxidative stress by TMAO(V) and DMA(V) contributes to their carcinogenicity in the rat liver and bladder.

Cytotoxic effects of various stressors on PC12 cells: involvement of oxidative stress and effect of antioxidants

In order to specifically elucidate the involvement of oxidative stress, the effects of various types of stressors and antioxidants on PC12 cells were examined. In this study, the following four stressors were studied in detail: free radicals generated from 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH), 4-hydroxynonenal (HNE), 7-ketocholesterol (KC), and arsenic trioxide (As2O3). Undifferentiated PC12 cells were treated with 50% lethal concentration (LC50) of these stressors, and subsequently the viability, apoptosis/necrosis ratio, reactive oxygen species (ROS) production, caspase-3 activity, and protection by antioxidants were measured to elucidate the underlying mechanisms that determine the action of these stressors on PC12 cells. The cytotoxicity did not correlate directly with the intracellular formation of ROS. For example, as compared to AAPH, As2O3 produced considerably smaller amounts of ROS at LC50. As observed in the cells incubated with As2O3, KC and HNE exerted cell toxicity, but with a moderate production of ROS. With the exception of HNE, the apoptosis/necrosis ratio of all the stressors evaluated by annexin V and propidium iodide assays increased with an increase in the incubation time at the LC50 values of these stressors. In accordance with apoptosis ratio, caspase activity was detected in the cells incubated with AAPH, As2O3, and KC, but not HNE at LC50 for 24 h. The protective effect of alpha-tocopherol, 17beta-estradiol, 2,3-dihydro-5-hydroxy-2,2-dipentyl-4,6-di-tert-butylbenzofuran (BO653), glutathione, and N-acetylcysteine (NAC) against cytotoxicity depended on the type of stressors. These antioxidants were found to be effective against the abovementioned stressors, except As2O3 against which only NAC was effective. These results suggest that the involvement of ROS and the protective effect of antioxidants depend on the type of stressors.

Environmental arsenic exposure and sputum metalloproteinase concentrations

Exposure to arsenic in drinking water is associated with an increased rate of lung cancer. The objective of this study was to determine whether arsenic exposure at relatively low concentrations (approximately 20 microg/L) is associated with changes in biomarkers of lung inflammation, as measured by the ratio of sputum metalloproteinase and antiproteinase activity. A total of 73 subjects residing in Ajo and Tucson, Arizona were recruited for this cross-sectional study. Tap water and first morning void urine were analyzed for arsenic. Matrix metalloproteinase 2 (MMP-2), 9 (MMP-9) and tissue inhibitor of metalloproteinase 1 (TIMP-1) were measured in induced sputum. Household tap water arsenic levels in Ajo (20.3+/-3.7 microg/L) were higher than in those Tucson (4.0+/-2.3 microg/L), as were mean urinary total inorganic arsenic levels (29.1+/-20.4 and 11.0+/-12.0 microg/L, respectively). Log-normalized MMP-2, MMP-9, and TIMP-1 concentrations in sputum were not significantly different between towns. However, after adjusting for town, asthma, diabetes, urinary monomethylarsonic acid/inorganic arsenic, and smoking history, total urinary arsenic was negatively associated with MMP-2 and TIMP-1 levels in sputum and positively associated with the ratio of MMP-2/TIMP-1 and MMP-9/TIMP-1 in sputum. Increased sputum proteinase/antiproteinase activity suggests a potential toxic mechanism for low-level arsenic exposure.

Decreased Nitric Oxide Production in the Rat Brain after Chronic Arsenic Exposure

Chronic arsenic exposure is associated with nervous system damage, vascular disease, hepatic and renal damage as well as different types of cancer. Alterations of nitric oxide (NO) in the periphery have been detected after arsenic exposure, and we explored here NO production in the brain. Female Wistar rats were exposed to arsenite in drinking water (4-5 mg/kg/day) from gestation, lactation and until 4 months of age. NOS activity, NO metabolites content, reactive oxygen species production (ROS) and lipid peroxidation (LPx) were determined in vitro in the striatum, and NO production was estimated in vivo measuring citrulline by microdialysis. Exposed animals showed a significantly lower response to NMDA receptor stimulation, reduction of NOS activity and decreased levels of nitrites and nitrates in striatum. These markers of NO function were accompanied by significantly higher levels of LPx and ROS production. These results provide evidence of NO dysfunction in the rat brain associated with arsenic exposure.

Arsenic carcinogenesis in the skin

Chronic arsenic poisoning is a world public health issue. Long-term exposure to inorganic arsenic (As) from drinking water has been documented to induce cancers in lung, urinary bladder, kidney, liver and skin in a dose-response relationship. Oxidative stress, chromosomal abnormality and altered growth factors are possible modes of action in arsenic carcinogenesis. Arsenic tends to accumulate in the skin. Skin hyperpigmentation and hyperkeratosis have long been known to be the hallmark signs of chronic As exposure. There are significant associations between these dermatological lesions and risk of skin cancer. The most common arsenic-induced skin cancers are Bowen's disease (carcinoma in situ), basal cell carcinoma (BCC) and squamous cell carcinoma (SCC). Arsenic-induced Bowen's disease (As-BD) is able to transform into invasive BCC and SCC. Individuals with As-BD are considered for more aggressive cancer screening in the lung and urinary bladder. As-BD provides an excellent model for studying the early stages of chemical carcinogenesis in human beings. Arsenic exposure is associated with G2/M cell cycle arrest and DNA aneuploidy in both cultured keratinocytes and As-BD lesions. These cellular abnormalities relate to the p53 dysfunction induced by arsenic. The characteristic clinical figures of arsenic-induced skin cancer are: (i) occurrence on sun-protected areas of the body; (ii) multiple and recrudescent lesions. Both As and UVB are able to induce skin cancer. Arsenic treatment enhances the cytotoxicity, mutagenicity and clastogenicity of UV in mammalian cells. Both As and UVB induce apoptosis in keratinocytes by caspase-9 and caspase-8 signaling, respectively. Combined UVB and As treatments resulted in the antiproliferative and proapoptotic effects by stimulating both caspase pathways in the keratinocytes. UVB irradiation inhibited mutant p53 and ki-67 expression, as well as increased in the number of apoptotic cells in As-BD lesions which resulted in an inhibitory effect on proliferation. As-UVB interaction provides a reasonable explanation for the rare occurrences of arsenical cancer in the sun-exposed skin. The multiple and recurrent skin lesions are associated with cellular immune dysfunction in chronic arsenism. A decrease in peripheral CD4+ cells was noticed in the inhabitants of arsenic exposure areas. There was a decrease in the number of Langerhans cells in As-BD lesion which results in an impaired immune function on the lesional sites. Since CD4+ cells are the target cell affected by As, the interaction between CD4+ cells and epidermal keratinocytes under As affection might be closely linked to the pathogenesis of multiple occurrence of arsenic-induced skin cancer. In this review, we provide and discuss the pathomechanisms of arsenic skin cancer and the relationship to its characteristic figures. Such information is critical for understanding the molecular mechanism for arsenic carcinogenesis in other internal organs.

Effects of individual and combined exposure to sodium arsenite and sodium fluoride on tissue oxidative stress, arsenic and fluoride levels in male mice

Arsenic and fluoride are potent toxicants, widely distributed through drinking water and food and often result in adverse health effects. The present study examined the effects of sodium meta-arsenite (100 mg/l in drinking water) and sodium fluoride (5 mg/kg, oral, once daily), administered either alone or in combination for 8 weeks, on various biochemical variables indicative of tissue oxidative stress and cell injury in Swiss albino male mice. A separate group was first exposed to arsenic for 4 weeks followed by 4 weeks of fluoride exposure. Exposure to arsenic or fluoride led to a significant depletion of blood delta-aminolevulinic acid dehydratase (ALAD) activity and glutathione (GSH) level. These changes were accompanied by increased level of blood and tissues reactive oxygen species (ROS) level. An increase in the level of liver and kidney thiobarbituric acid reactive substance (TBARS) along with a concomitant decrease in the activities of superoxide dismutase (SOD), catalase, and glutathione peroxidase (GPx) and reduced GSH content were observed in both arsenic and fluoride administered mice. The changes were significantly more pronounced in arsenic exposed animals than in fluoride. It was interesting to observe that during combined exposure the toxic effects were less pronounced compared to the effects of arsenic or fluoride alone. In some cases antagonistic effects were noted following co-exposure to arsenic and fluoride. Arsenic and fluoride concentration increased significantly on exposure. Interestingly, their concentration decreased significantly on concomitant exposure for 8 weeks. However, the group which was administered arsenic for 4 weeks followed by 4 weeks of fluoride administration showed no such protection suggesting that the antagonistic effect of fluoride on arsenic or vice versa is possible only during interaction at the gastro intestinal sites. These results are new and interesting and require further exploration.

Dimethylarsinic acid: Results of chronic toxicity/oncogenicity studies in F344 rats and in B6C3F1 mice

Dimethylarsinic acid (DMA(V), cacodylic acid), a foliar herbicide, was administered in the diet to B6C3F1 mice (at dose levels of 0, 8, 40, 200, and 500 ppm) and to F344 rats (at dose levels of 0, 2, 10, 40, and 100 ppm) for 2 years, according to US EPA guidelines. In mice, there were no treatment-related tumors observed at any site. Treatment-related progressive glomerulonephropathy and nephrocalcinosis were observed in the kidneys in both sexes. The incidence of vacuolation of the epithelium in the urinary bladder was increased in both sexes, but was not associated with cytotoxicity, necrosis or hyperplasia. Based on non-neoplastic lesions found in the urinary bladder, the NOEL for mice was assessed to be 40 ppm in males and 8 ppm in females. In rats, treatment-related mortality occurred early in the study in five males in the 100 ppm group and in one male in the 40 ppm group. Papillomas and carcinomas with degeneration of the urothelium, necrosis and urothelial cell hyperplasia, were found in the urinary bladders of both sexes. In male rats, one papilloma was found in each of the 10 and 40 ppm groups; one urothelial cell carcinoma was found in the 2 ppm group and two in the 100 ppm group. Four papillomas and six urothelial cell carcinomas were found in the female 100 ppm group. Non-neoplastic treatment-related kidney lesions were confined to the 40 and 100 ppm levels and included necrosis, pyelonephritis, medullary nephrocalcinosis and tubular cystic dilation, hyperplasia of the epithelial lining of the papilla, and pelvic urothelial cell hyperplasia. All of these kidney changes appear to be related to an increase in the aging nephropathy of the rat. Dose-related increases in the height of the thyroid follicular epithelium were also noted in males and females, however, such changes reflect an adaptive response of the thyroid to decreased levels of circulating thyroid hormone, rather than an adverse effect. Based on the kidney and bladder lesions, the NOEL for non-neoplastic and neoplastic lesions was considered to be 10 ppm in males and females. Based on these studies, DMA(V) is carcinogenic only in rats and only at relatively high doses, with the urinary bladder as the target organ. Female rats appear to be more sensitive to the effects of DMA(V) than male rats. DMA(V) is not carcinogenic in mice.

Metabolism of arsenic in Drosophila melanogaster and the genotoxicity of dimethylarsinic acid in the Drosophila wing spot test

Inorganic arsenic is nongenotoxic in the Drosophila melanogaster wing somatic mutation and recombination test (SMART). Recent evidence in mammalian systems indicates that methylated metabolites of arsenic are more genotoxic than inorganic arsenic. Thus, we hypothesized that inorganic arsenic is nongenotoxic in Drosophila because they are unable to biotransform arsenic to methylated forms. In the present study, we fed trivalent and pentavalent inorganic arsenic to Drosophila larvae and adults and measured the production of methylated derivatives. No biomethylated arsenic species were found in the organisms or in the growth medium, which suggests that Drosophila are unable to biomethylate inorganic arsenic. Exposure of Drosophila to the methylated arsenic derivative dimethylarsinic acid (DMA(V)) resulted in incorporation of this organoarsenic compound without demethylation. In addition, we used the SMART wing spot assay, which measures loss of heterozygosity (LOH) resulting from gene mutation, chromosomal rearrangement, chromosome breakage, and chromosome loss, to evaluate the genotoxicity of DMA. DMA by itself induced significant increases in the frequency of total spots, small spots, and large single spots. These results are consistent with the important role of arsenic biomethylation as a determinant of the genotoxicity of arsenic compounds. The absence of biomethylation in Drosophila could explain the lack of genotoxicity for inorganic arsenic and the genotoxicity of methylated arsenic species in the SMART wing spot assay.

Co-administration of zinc and n-acetylcysteine prevents arsenic-induced tissue oxidative stress in male rats

Arsenic is a widespread environmental toxicant that may cause neuropathy, skin lesions, vascular lesions and cancer upon prolonged exposure. Improving nourishment like supplementation of micronutrients, antioxidants, vitamins and amino acids could be able to halve the risk in those who were previously the poor nourished. The present study was planned to investigate the preventive effects of zinc and n-acetylcysteine (NAC) supplementation either alone or in combination with arsenic on selected biochemical variables indicative of oxidative stress and liver injury in male rats. For 3 weeks 25 male wistar rats were exposed to arsenic as sodium arsenite (2 mg/kg, orally through gastric intubation) either alone or in combination with NAC (10 mg/kg, intraperitoneally), zinc (5 mg/kg, orally) or zinc plus NAC. Animals were sacrificed 24h after the last dosing for various biochemical parameters. Concomitant administration of zinc with arsenic showed remarkable protection against blood delta-aminolevulinic acid dehydratase (ALAD) activity as well as providing protection to hepatic biochemical variables indicative of oxidative stress (like thiobarbituric acid reactive substances (TBARS) level, catalase) and tissue injury. NAC supplementation on the other hand, was moderately effective in protecting animals from the toxic effects of arsenic. Interestingly, concomitant administration of zinc and NAC was most effective compared to zinc or NAC in eliciting above-mentioned protective effects. The above results suggest significant protective value of combined zinc and NAC administration in acute arsenic exposure.

Metal ions and carcinogenesis

Metals are essential for the normal functioning of living organisms. Their uses in biological systems are varied, but are frequently associated with sites of critical protein function, such as zinc finger motifs and electron or oxygen carriers. These functions only require essential metals in minute amounts, hence they are termed trace metals. Other metals are, however, less beneficial, owing to their ability to promote a wide variety of deleterious health effects, including cancer. Metals such as arsenic, for example, can produce a variety of diseases ranging from keratosis of the palms and feet to cancers in multiple target organs. The nature and type of metal-induced pathologies appear to be dependent on the concentration, speciation, and length of exposure. Unfortunately, human contact with metals is an inescapable consequence of human life, with exposures occurring from both occupational and environmental sources. A uniform mechanism of action for all harmful metals is unlikely, if not implausible, given the diverse chemical properties of each metal. In this chapter we will review the mechanisms of carcinogenesis of arsenic, cadmium, chromium, and nickel, the four known carcinogenic metals that are best understood. The key areas of speciation, bioavailability, and mechanisms of action are discussed with particular reference to the role of metals in alteration of gene expression and maintenance of genomic integrity.

Specific induction of oxidative stress in terminal bronchiolar Clara cells during dimethylarsenic-induced lung tumor promoting process in mice

The induction of oxidative stress in pulmonary cells during the process of lung tumor promotion by dimethylarsinic acid (DMA), a main metabolite of inorganic arsenics in mammals, was examined by immunohistochemical analysis using a specific antibody against 4-hydroxy-2-nonenal (4HNE) adducts, which are major aldehydic metabolites of lipid peroxidation. We demonstrated that 4HNE-modified proteins existed specifically in the secretory granules in terminal bronchiolar Clara cells. Furthermore, the degree of positive staining increased with the duration of DMA administration. Transmission electron microscopy revealed morphological changes in the Clara cells of DMA-treated mice. These results suggest that Clara cells are the major target cell for DMA-induced oxidative stress and that the cells may play an important role in the lung tumor promotion process in mice.

Combined efficacies of dl-α-lipoic acid and meso 2,3 dimercaptosuccinic acid against arsenic induced toxicity in antioxidant systems of rats

Health hazards caused by heavy metals have become a great concern to the population. Arsenic as an environmental agent is considered to be a toxic substance due to its carcinogenic potential in humans. Since arsenic compounds might exert their toxicity by the generation of reactive oxygen species, we have evaluated the effect of both DL-alpha-lipoic acid (LA) and meso 2,3 dimercapto succinic acid (DMSA) on the antioxidants and lipid peroxidation in arsenic treated rats. The objective of the study was to determine whether DL-alpha-lipoic acid and meso 2,3 dimercapto succinic acid could rehabitate antioxidant depletion and damage to biomolecules in protection against oxidative insults. A significant increase in the levels of reactive oxygen species formation and lipid peroxidation and decrease in the activities of antioxidant enzymes were observed in arsenic exposed rats. Supplementation of DL-alpha-lipoic acid and meso 2,3 dimercapto succinic acid to arsenic fed rats significantly increased the activities of superoxide dismutase, catalase, glutathione peroxidase with elevation in the levels of reduced glutathione, total sulfhydryl, ascorbic acid and alpha-tocopherol. In addition, significant decrease in the levels of reactive oxygen species formation and lipid peroxidation was also observed in our study. From our results, we conclude that DL-alpha-lipoic acid and meso 2,3 dimercapto succinic acid play a synergistic role in decreasing arsenic induced oxidative damage by elevating the antioxidant status in liver and kidney.

Arsenic induced blood and brain oxidative stress and its response to some thiol chelators in rats

Chronic arsenic toxicity is a widespread problem, not only in India and Bangladesh but also in various other regions of the world. Exposure to arsenic may occur from natural or industrial sources. The treatment that is in use at present employs administration of thiol chelators, such as meso 2,3-dimercaptosuccinic acid (DMSA) and sodium 2,3-dimercaptopropane 1-sulfonate (DMPS), which facilitate its excretion from the body. However, these chelating agents are compromised with number of limitations due to their lipophobic nature, particularly for their use in cases of chronic poisoning. During chronic exposure, arsenic gains access into the cell and it becomes mandatory for a drug to cross cell membrane to chelate intracellular arsenic. To address this problem, analogs of DMSA having lipophilic character, were examined against chronic arsenic poisoning in experimental animals. In the present study, therapeutic efficacy of meso 2,3-dimercaptosuccinic acid (DMSA), sodium 2,3-dimercaptopropane 1-sulfonate (DMPS), monoisoamyl DMSA (MiADMSA) were compared in terms of reducing arsenic burden, as well as recovery in the altered biochemical variables particularly suggestive of oxidative stress. Adult male Wistar rats were given 100-ppm arsenic for 10 weeks followed by chelation therapy with the above chelating agents at a dose of 50 mg/Kg (orally) once daily for 5 consecutive days. Arsenic exposure resulted in marked elevation in reactive oxygen species (ROS) in blood, inhibition of ALAD activity and depletion of GSH. These changes were accompanied by significant decline in blood hemoglobin level. MiADMSA was the most effective chelator in reducing ROS in red blood cells, and in restoring blood ALAD compared to two other chelators. Brain superoxide dismutase (SOD) and glutathione peroxidase (GPx) decreased, while ROS and TBARS increased significantly following arsenic exposure. There was a significant increase in the activity of glutathione-S-transferase (GST) with a corresponding decline in its substrate i.e. glutathione. Among all the three chelators, MiADMSA showed maximum reduction in the level of ROS in brain. Additionally, administration of MiADMSA was most effective in counteracting arsenic induced inhibition in brain ALAD, SOD and GPx activity. Based on these results and in particular higher metal decorporation from blood and brain, we suggest MiADMSA to be a potential drug of choice for the treatment of chronic arsenic poisoning. However, further studies are required for the choice of appropriate dose, duration of treatment and possible effects on other major organs.

Therapeutic Value ofHippophae rhamnoidesL. Against Subchronic Arsenic Toxicity in Mice

The present study was planned to investigate the therapeutic efficacy of Hippophae rhamnoides L. against the toxic effects of arsenic in mice. H. rhamnoides L. is used as an herbal remedy for gastric ulcers, burns, and some skin and allergic diseases. Twenty-five Swiss albino mice were exposed to arsenic (25 ppm) in drinking water for 3 months. After 3 months different fruit extracts of H. rhamnoides L. (500 mg/kg for 10 days) were administered, the animals were sacrificed, and blood and tissues were assayed for various biochemical indicators of oxidative stress and whether arsenic was removed from tissues. Treatment with different fruit extracts of H. rhamnoides L. showed significant protection from arsenic inhibition of blood delta-aminolevulinic acid dehydratase activity and restored blood reduced glutathione levels. Other hematologic variables like white blood cell counts, hemoglobin, and hematocrit were partially protected by supplementation with a water extract of H. rhamnoides L. (HF-WRT). Significant protection was also observed in altered hepatic, renal, and brain reduced/ oxidized glutathione ratio and thiobarbituric acid-reactive substances levels. The aqueous extract of H. rhamnoides L. (HF-WRT) also provided protection against parameters indicative of liver injury such as aspartate aminotransferase, alanine aminotransferase, and alkaline phosphatase activities. There was also no effect on blood and tissue arsenic concentrations observed except some moderate depletion of blood arsenic concentrations, suggesting that the drug has no ability to chelate intracellular arsenic. It can be concluded from these results that post-treatment with an aqueous extract of H. rhamnoides L. (HF-WRT) significantly protects against arsenic-induced oxidative stress but does not chelate arsenic, suggesting it may have a beneficial role as a supplementing agent during chelation of arsenic by other means.

Effect of chronic intake of arsenic-contaminated water on liver

The hepatotoxic effect of arsenic when used in therapeutic dose has long been recognized. We described the nature and degree of liver involvement and its pathogenesis due to prolonged drinking of arsenic-contaminated water in West Bengal, India. From hospital-based studies on 248 cases of arsenicosis, hepatomegaly was found in 190 patients (76.6%). Non cirrhotic portal fibrosis was the predominant lesions in 63 out of 69 cases who underwent liver biopsy. The portal fibrosis was characterized by expansion of portal zones with streaky fibrosis, a few of which contained leash of vessels. However, portal hypertension was found in smaller number of cases. A cross-sectional epidemiological study was carried out on 7683 people residing in arsenic-affected districts of West Bengal. Out of these, 3467 and 4216 people consumed water-containing arsenic below and above 0.05 mg/l, respectively. Prevalence of hepatomegaly was significantly higher in arsenic-exposed people (10.2%) compared to controls (2.99%, P < 0.001). The incidence of hepatomegaly was found to have a linear relationship proportionate to increasing exposure of arsenic in drinking water in both sexes (P < 0.001). In an experimental study, BALB/C mice were given water contaminated with arsenic (3.2 mg/l) ad libitum for 15 months, the animals being sacrificed at 3-month intervals. We observed progressive reduction of hepatic glutathione and enzymes of anti-oxidative defense system associated with lipid peroxidation. Liver histology showed fatty infiltration at 12 months and hepatic fibrosis at 15 months. Our studies show that prolong drinking of arsenic-contaminated water is associated with hepatomegaly. Predominant lesion of hepatic fibrosis appears to be caused by arsenic induced oxystress.

Implications of oxidative stress and hepatic cytokine (TNF-alpha and IL-6) response in the pathogenesis of hepatic collagenesis in chronic arsenic toxicity

INTRODUCTION

Noncirrhotic portal fibrosis has been reported to occur in humans due to prolonged intake of arsenic contaminated water. Further, oxystress and hepatic fibrosis have been demonstrated by us in chronic arsenic induced hepatic damage in murine model. Cytokines like tumor necrosis factor alpha (TNF-alpha) and interleukin 6 (IL-6) are suspected to play a role in hepatic collagenesis. The present study has been carried out to find out whether increased oxystress and cytokine response are associated with increased accumulation of collagen in the liver due to prolonged arsenic exposure and these follow a dose-response relationship.

METHODS

Male BALB/c mice were given orally 200 microl of water containing arsenic in a dose of 50, 100, and 150 mug/mouse/day for 6 days a week (experimental group) or arsenic-free water (<0.01 microg/l, control group) for 3, 6, 9 and 12 months. Hepatic glutathione (GSH), protein sulfhydryl (PSH), glutathione peroxidase (GPx), Catalase, lipid peroxidation (LPx), protein carbonyl (PC), interleukin (IL-6), tumor necrosis factor (TNF-alpha), arsenic and collagen content in the liver were estimated from sacrificed animals.

RESULTS

Significant increase of lipid peroxidation and protein oxidation in the liver associated with depletion of hepatic thiols (GSH, PSH), and antioxidant enzymes (GPx, Catalase) occurred in mice due to prolonged arsenic exposure in a dose-dependent manner. Significant elevation of hepatic collagen occurred at 9 and 12 months in all the groups associated with significant elevation of TNF-alpha and IL-6. However, arsenic level in the liver increased progressively from 3 months onwards. There was a positive correlation between the hepatic arsenic level and collagen content (r = 0.8007), LPx (r = 0.779) and IL-6 (r = 0.7801). Further, there was a significant negative correlation between GSH and TNF-alpha (r = -0.5336)) and LPx (r = -0.644).

CONCLUSION

Increasing dose and duration of arsenic exposure in mice cause progressive increase of oxystress and elevation of cytokines associated with increasing level of collagen in the liver.

Brain regional responses in antioxidant system to α-lipoic acid in arsenic intoxicated rat

Impaired antioxidant defense mechanisms and oxidative stress are implicated in the pathogenesis of arsenic toxicity. Our study was designed to determine whether alpha-lipoic acid, which has been shown to have substantial antioxidant properties, when administered (70 mg/kg body weight) once daily for 60 days along with arsenic (100 ppm sodium arsenite mixed in drinking water) would prevent arsenic-induced changes in antioxidant defense system, superoxide dismutase (SOD-total SOD, Mn SOD, Cu/Zn SOD), catalase (CAT) and glutathione peroxidase (GSH-PX) in rat brain regions such as cortex, hypothalamus, striatum, cerebellum and hippocampus. The present study also examined the effect of alpha-lipoic acid over arsenic-induced oxidant production and lipid peroxidation level (LPO) in discrete brain regions of rats. The cortex, striatum and hippocampus showed greater decreases in GSH-Px enzyme activity than cerebellum and hypothalamus with arsenic exposure. Striatum had the greatest percentage of decreased activities of total SOD and Mn SOD, whereas cortex had the greatest percentage decrease in the activity of Cu/Zn SOD in arsenic-alone treated rats. Hypothalamus and cerebellum exhibited the lowest catalase activity among all tested regions in arsenic-only treated rats. Rate of dichlorofluorescin oxidation, an indication of reactive oxygen species and other intracellular oxidants production was increased with arsenic exposure in all brain regions studied. Cortex, hippocampus and striatum exhibited greater increase of LPO levels than cerebellum and hypothalamus. SOD, CAT, GSH-Px activities were upregulated in arsenic plus lipoic acid treated versus arsenic-only treated rats. Also, simultaneous lipoic acid treatment along with arsenic proved to be sufficient in reducing oxidant production and LPO level in all rat brain regions. Our results demonstrate that arsenic-induced deficits in antioxidant enzyme activities and increase in oxidant production and lipid peroxidation level in brain regions can be overcome through simultaneous treatment with lipoic acid.

The role of trivalent dimethylated arsenic in dimethylarsinic acid-promoted skin and lung tumorigenesis in mice: tumor-promoting action through the induction of oxidative stress

We investigated the relationship between lung- and skin-tumor promotion and oxidative stress caused by administration of dimethylarsinic acid (DMA(V)) in mice. The incidence of lung tumors induced by lung tumor initiator (4NQO) and DMA(V) were, as well as 8-oxo-2'-deoxyguanosine (8-oxodG), suppressed by cotreatment with (-)epigallocatechin gallate (EGCG). When mice were topically treated with trivalent dimethylated arsenic (DMA(III)), a further reductive metabolite of DMA(V), not only an increase in skin tumors but also an elevation of 8-oxodG in epidermis were observed. These results suggest that tumor promotion due to DMA(V) administration is mediated by DMA(III) through the induction of oxidative stress.

DNA–protein cross-links and sister chromatid exchanges induced by dimethylarsinic acid in human fibroblasts cells

Biotransformation of inorganic arsenic to form both methylarsinic acid (MA) and dimethylarsinic acid (DMA) has traditionally been considered as a mechanism to facilitate the detoxification and excretion of arsenic. However, the methylation of inorganic arsenic as a detoxification mechanism has been questioned due to recent studies revealing an important role of organic arsenic in the induction of genetic damage. In a previous report a reduction of DNA migration after treatment of cells with DMA was described. In order to further evaluate the possible induction of protein-DNA adducts, an experiment was performed taking into account other parameters and modifications of the standard alkaline comet assay. In addition, the results obtained with the comet assay were compared with those obtained by analyzing the induction of sister chromatid exchanges (SCEs). SCE frequencies were significantly increased in treated cells in relation to controls (p<0.001). Furthermore, in the standard alkaline comet assay, as well as in the control assay for proteinase K treatment, a significant dose-dependent reduction in tail moment was observed. Nevertheless, the post-treatment with proteinase K induced the release of proteins joined to the DNA and consequently, a dose-dependent increment in DNA migration was observed (p<0.001). These results suggest that DNA-protein cross-links may be an important genotoxic effect induced by dimethylarsinic acid in human MRC-5 cells.

Arsenic antagonism studies with monoisoamyl DMSA and zinc in male mice

Administration of zinc either alone or in combination with monoisoamyl dimercaptosuccinic acid (DMSA) during and post-arsenic exposure was investigated in male mice. The animals were administered 2mgkg(-1) arsenic as sodium arsenite, intraperitoneally, once daily for 5 days either alone or in combination with 10mgkg(-1), zinc (as zinc acetate, orally), 50mgkg(-1) monoisoamyl dimercaptosuccinic acid (MiADMSA) given orally (p.o.), 2h after arsenic administration. Another group of arsenic treated animals was given both zinc (10mgkg(-1)) and MiADMSA (50mgkg(-1), p.o.). Animals were sacrificed 24h after the last dose. In another set of experimentation, arsenic pre-exposed mice (2mgkg(-1), i.p. for 5 days) were treated with saline, zinc, MiADMSA or zinc plus MiADMSA for next 3 days and sacrificed thereafter. Exposure to arsenic led to a significant inhibition of blood δ-aminolevulinic acid dehydratase (ALAD), depletion of glutathione (GSH) level and marginal elevations of zinc protoporphyrin (ZPP). Arsenic exposure caused a significant decrease in hepatic and renal GSH level and an increase in liver oxidized glutathione (GSSG) and liver and kidney thiobarbituric acid reactive substance (TBARS) levels. Concomitant administration of zinc with arsenic provided significant protection to blood ALAD activity while, GSH and ZPP levels remained unaltered. Co-administration of MiADMSA with arsenic significantly prevented accumulation of arsenic in blood, liver and kidney while, zinc had no effect on tissue arsenic concentration. Combined administration of zinc and MiADMSA had no major additional beneficial effects over their individual effects. Interestingly, post-arsenic exposure treatment with MiADMSA provided significant recovery in blood ALAD activity while, zinc supplementation alone had no effect. The best results however, were obtained when MiADMSA was administered along-with zinc. Most of the biochemical variables indicative of hepatic oxidative stress responded favorably to MiADMSA treatment while, zinc administration had no effect. Administration of MiADMSA significantly depleted arsenic concentration from the soft tissues while, combined zinc and MiADMSA had no additional beneficial effect over the individual effect of MiADMSA. The results thus lead us to conclude that in order to achieve best effects of chelation therapy, co-administration of zinc with chelator might be preferred. However, detailed experimental studies with variable doses and after chronic arsenic exposure are required.

Immunohistochemical analysis of oxidative DNA damage in arsenic-related human skin samples from arsenic-contaminated area of China

The appearance of 8-oxo-2'-deoxyguanosine (8-oxodG) was examined immunohistochemically using an 8-oxodG-monoclonal antibody in 28 cases of arsenic-related human skin tumors and in 20 cases of arsenic-unrelated human skin cancer to determine if the induction of oxidative stress participates in skin tumorigenesis caused by arsenics. The rate of 8-oxodG-positive was significantly higher in arsenic-related human skin cancer (28 of 28, 100%) than in arsenic-unrelated human skin cancer (3 of 20, 15%, P<0.01 by Chi2 test). Moreover, in all the arsenic-related skin samples, 8-oxodG was detected not only in tumor tissues but also in keratosis and normal tissues. These results suggest that the induction of oxidative stress may play an important role in arsenic carcinogenesis.

Oxidative mechanism of arsenic toxicity and carcinogenesis

Arsenic is a known toxin and carcinogen that is present in industrial settings and in the environment. The mechanisms of disease initiation and progression are not fully understood. In the last a few years, there has been increasing evidence of the correlation between the generation of reactive oxygen species (ROS), DNA damage, tumor promotion, and arsenic exposure. This article summarizes the current literature on the arsenic mediated generation of ROS and reactive nitrogen species (RNS) in various biological systems. This article also discusses the role of ROS and RNS in arsenic-induced DNA damage and activation of oxidative sensitive gene expression.